During combat, the situation might arise where it is necessary to breach a "safe" lane through either friendly or enemy minefields in order to facilitate a retreat or an assault on enemy positions. By safe, it is meant that any mines in the lane must either be removed, rendered nonfunctional, or neutralized through induced triggering, thus allowing passage of troops and vehicles through the minefield without incident.
A survey of current minefield detection and breaching methods indicates that most existing mine-clearing techniques are based on either mechanical devices such as ploughs, rollers and flails, or on explosive devices such as the high-explosive (HE) line charge and the fuel-air explosive (FAE) canister array.
The high-explosive line charge is exemplified by the U.K. "Giant Viper" system which consists of a 183 m long hose filled with PE6/A1 high explosive. Weighing almost 1500 kg, the Giant Viper is carried aboard a trailer and towed to the minefield by an armoured vehicle. It is projected across the minefield from a standoff of 100 m by a flight vehicle powered by eight rocket motors. Three arresting parachutes straighten, stabilize and decelerate the hose as it falls across the minefield. A delayed fuse, activated by the parachutes, then detonates the explosive-filled hose producing a blast wave which triggers single-impulse pressure sensitive mines within a distance of 3.5 m from the charge.
The FAE canister system is the basis of the U.S. Surface Launched Unit Fuel-Air Explosive (SLUFAE). The SLUFAE system consists of 30 rocket-propelled canisters mounted on a tracked cargo vehicle. Each canister contains 38.5 kg of liquid propylene oxide fuel. These are sequentially launched from a 700 m standoff and follow parachute retarded trajectories to land along a line spanning the minefield. Upon impact, the fuel in each canister is dispersed to form an explosive fuel droplet-air cloud which is subsequently detonated by a small explosive charge. The detonation of each cloud produces a blast wave capable of activating surface-laid single-impulse pressure sensitive mines within a circular area 20 m in diameter. The SLUFAE device is also intended to neutralize buried single-impulse mines, an operation which requires substantially higher specific impulses. For mines buried 15 cm below grade, a SLUFAE canister is capable of clearing a 12 m diameter circle. In such a minefield, the 30 canisters are deployed in an overlapping linear array to clear a path 160 m long and 8 m wide.
Both minefield breaching systems described above are inadequate in terms of operational reliability, effectiveness and cost. Launching the high-explosive line charge across a minefield is a difficult and hazardous operation with a relatively high occurrence of misfires. Furthermore, the detonation of the high-explosive charge produces a "skip zone" of decreased pressure and impulse, parallel to and about 1 m off the charge axis, where mines might not be triggered.
From a fundamental point of view, the use of high explosives is not the most attractive option for breaching purposes. This is true for two reasons. First, a significant fraction of the high-explosive material is oxygen, which must be launched over the minefield along with the fuel component, despite the abundance of readily available oxygen along the intended breach lane. This results in a larger payload having to be deployed than would be the case if ambient oxygen was consumed in the reaction. Second, high explosives produce a blast field with pressures and impulses which far exceed those required for breaching in the near field, but which fall off rapidly with increasing distance from the charge and quickly becomes unsatisfactory for breaching purposes. In other words, the distribution of available energy or "energy density" is far from optimum.
An attractive alternative to high explosives, which avoids these fundamental shortcomings, is fuel-air explosives. With this type of explosive, atmospheric oxygen is consumed during the detonation reaction. As well, the fuel is distributed over a large area, resulting in a charge of lower energy density, but making more effective use of the fuel. Although the U.S. SLUFAE system enjoys these advantages over the Giant Viper, it too suffers drawbacks, but of a different nature. For example, the system requires high deployment accuracy in order to ensure that the canisters land properly spaced along a line across the minefield. With the canisters being parachute retarded, this tends to be a difficult feat, particularly in the presence of any cross winds. As a result, the design cloud overlap must be substantial in order to eliminate skip zones where mines would not be triggered. This creates yet another problem; namely, that the hot combustion products resulting from the detonation of one cloud tend to prematurely ignite the fuel droplet-air cloud produced by the neighbouring canister. The mere fact that SLUFAE attempts to approximate a lane by a series of overlapping circular clouds also means that the fuel is not being used efficiently.